Apparatus for centrifugal casting

ABSTRACT

A method and apparatus for the centrifugal casting of articles having non-uniform mass distributions with respect to an axis of rotation; the method comprises the steps of forming a sand mold in a cylindrical centrifuge, providing cavities in the sand mold adjacent the portions of the mold surface corresponding to that portion of the article to be formed which will have a reduced mass content with respect to the portion of the article formed on the opposite side of the axis of rotation of the centrifuge; conduits connect the respective cavities to the interior of the centrifuge so that casting material introduced into the mold may be fed into the respective cavities; the cross-sectional area of the conduits is chosen to meter the feeding of casting material into the cavities so that when the centrifuge is rotated the article being formed will be maintained in rotational equilibrium with respect to its axis of rotation.

United States Patent 1191 Schroll et al.

3,741,283 June 26, 1973 APPARATUS FOR CENTRIFUGAL CASTING Primary ExaminerJ. Spencer Overholser Assistant Examiner-John S. Brown [75] Inventors: Josef Schroll; Werner Sroke, both of Attorney-Cushman, Darby & Cushman Rostock, Germany [57] ABSTRACT A method and apparatus for the centrifugal casting of articles having non-uniform mass distributions with respect to an axis of rotation; the method comprises the steps of forming a sand mold in a cylindrical centrifuge, providing cavities in the sand mold adjacentthe portions of the mold surface corresponding to that portion u ay n 3 m e G m C bf ra wh .l n0 k 4 ICLS m Sal-5H Eocs VRO e e N m a 1. a w kw A HA .1 .l] 3 2 7 2 Foreign Application Priority Data Oct. 16, 1970 Jan. 29, 1971 of the article to be formed which will have a reduced E tG ....WP3lb $0 ii f g P 2] 1 mass content with respect to the portion of the article formed on the opposite side of the axis of rotation of the centrifuge; conduits connect the respective cavities to the interior of the centrifuge so that casting material introduced into the mold may be fed into the respective cavities; the cross-sectional area of the conduits is chosen to meter the feeding of casting material into the 41 9 6 400 l ll 4m M A UZ m m w. 7 9

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cavities so that when the centrifuge is rotated the article being formed will be maintained in rotational equilibrium with respect to its axis of rotation.

[56] References Cited 1 UNITED STATES PATENTS 5 Claims 1 Dra in Fi ure 1,037,859 9/1912 Burk 164/332 w 3 3 2,192,787 3/1940 164/333 x PAIENlEnJuuzars 174L283 INVENTOR$ dosEPH 509204 4 WERNER Spa 5 ATTORNEYS APPARATUS FOR CENTRIFUGAL CASTING The present invention relates to a method and'apparatus for centrifugal casting of articles in sandlined molds, and more particularly, to a method and apparatus for forming articles having a non-uniform mass distribution with respect to the axis of rotation of the articles.

BACKGROUND OF THE INVENTION The production of articles by centrifugal casting in sand-lined cast-iron molds is well known and has been used to form articles which are generally symmetric about one of their dimensional axes. Difficulties have been experienced however, when centrifugal casting methods and apparatus have been employed to form articles which have asymmetricmass distributions with respect to rotational axis of the forming centrifuge. The cause of such difficulties, of course, has been the absence of rotational equilibrium of the casting material as it is accumulated in the centrifugeto form the article. The problem of balancing the molding material during the centrifuge process has been particularly acute when the casting of large structures has been attempted. Even when centrifugal casting has been attempted in the production of small articles, considerable machining of the article subsequent to its casting has been required where precise engineering tolerances have been desired. Moreover, even if the'forces tending to destroy the rotational equilibrium of the centrifugal casting apparatus could be controlled so as to avoid damage to the centrifuge itself, it has not, prior to the present invention, been possible to effectively counteract the effect of the equilibrium destroying'forces on the composition used to form the mold pattern itself, such as sand for example.

In the past, systems have been proposed wherein fixed masses have been utilized to balance centrifugal casting machines. However, such systems have suffered the disadvantage that they could not be made to operate automatically so that, as a result, the casting process would have to be halted to adjust the masses periodically which adversely affected the quality of the cast article.

The method and apparatus of the present invention avoids the foregoing disadvantages by providing a centrifugal casting system which substantially lessens if not entirely eliminates any rotational imbalancesthat may occur as a result of the non-uniformity of the articles being manufactured.

SUMMARY OF THE INVENTION 1 The method of the present invention consists in forming pockets or cavities in the mold material adjacent the portions of the mold surfacecorresponding to the portions of the article to be formed which have a reduced mass with respect to that portion of the article which is diametrically opposite the reduced portion so that rotational equilibrium about the axis of rotation of the centrifuge can be obtained when casting material is introduced into the mold. These balancing cavities may be spaced radially outwardly from the axis of rotation a predetermined distance so that their volume may actually be less than that which would be necessary were they located at the same distance from the axis of rotation as that portion of the article on the opposite side for which these cavities are supplied as counterbalances. Channels 0r conduits are formed in the mold material in order to connect these pockets or cavities to the interior surface of the mold pattern where the casting material is initially introduced. The crosssectional area of these conduits is selected so that the balancing cavity will be filled during the casting process at a rate sufficient to maintain the rotational equilibrium of the article being formed. Additionally, the connecting conduits are shaped so that the resulting masses that are cast may be easily removed from the finished article without detracting from the quality of the casting article.

According to the present invention, the cavities and associated connecting channels may be formed in a sand mold by means of preformed pattern containers which are constructed from sheet metal materials or from materials which burn without having residues when contacted by the molten casting material. The use of preformed patterns to form the balance cavities will, of course, result in increased accuracy in the volumetric dimensions of the cavities and associated channels so that the highest possible degree of rotational equilibrium can be achieved.

With the foregoing arrangement, the rotational imbalances that occur in the casting of articles having non-uniform mass distributions can be minimized if not entirely eliminated so that the centrifugal casting apparatus will properly function without being subjected to uneven stresses that would tend to damage the rotating apparatus such as the motor and bearing mounts. Also, a superior article can be formed by use of the method and apparatus of the present invention since the solidification of the cast article will be carried out under substantially uniform centrifugal forces.

It is a principal object of the present invention, therefore, to provide a method for the centrifugal casting of articles which have asymmetric mass distributions with respect to their axis of rotation and which will result in the formation of an article of improved quality and which can be carried out more efficiently than has heretofore been possible.

Another object of the present invention resides in the provision of a mold pattern which automatically compensates for the uneven mass distribution of an article as it is being formed. A

Further additional objects and attendant advantages of the present invention will become apparent as consideration is given to the following detailed description and the accompanying drawing in which the single FIG- URE is a cross-sectional view of a centrifuging head containing a sand mold pattern formed according to the principles of the present invention and a cast article having a non-uniform mass distribution with respect to its axis of rotation.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is illustrated a cross-sectional view of a centrifuge head 1 supported on a pair of rollers 7. The rollers may be driven by a conventional power source through gears or pulleys to impart rotary motion to the centrifuge head 1 to rotate the head about its longitudinal axis generally indicated at 8. In the embodiment illustrated, the centrifuge head 1 is generally cylindrical in shape and is being used to form a hollow cylindrical article 4. A cylindrical collar 2 of cast-iron is located within the centrifuge head 1 and the sand-lining making up the mold pattern 3 is formed on the interior of the collar 2. The centrifugally molded article 4 is a body having an asymmetric shape on its exterior surfaces as the lower portion 9 has a nonuniform mass distribution with respect to the upper portion 10. ln the process of centrifuging such bodies, a considerable rotational imbalance occurs due to the non-uniform mass distribution. Such imbalance can cause considerable damage to the centrifuging apparatus and can also result in spoiled castings since the fluid casting material will tend to gravitate towards the heavier portion of the article resulting in the deformation of the mold pattern 3 itself.

The present invention provides a method and means for compensating for such imbalance by providing balancing cavities as at in the areas of the sand pattern 3 adjacent to the portions of the article having a reduced mass with respect to the portion of the article diametrically opposite to such reduced portions. The cavities may be located radially outwardly fromthe inner surface 11 of the sand pattern and are connected to the inner surface by means of channels or conduits,

one of which is indicated at 6, which extend generally radially from the axis of rotation of the centrifuge head 1. Sand pattern 3 is formed with its exterior surface 12 engaging the collar 2 of the centrifuge head 1 and with its inner surface 11 forming the pattern for shaping the article to be cast. The pattern may be obtained by the use of a sheet metal form which is removedprior to casting or preferably by the use of pattern forming materials which will burn without leaving a residue when contacted by the molten casting material. An example of such a material is polystrene plastic which'when exposed to moltencasting material will produce mostly gaseous combustion products which entrap the ash produced by the combustion and escape through the porous sand. In this latter arrangement, of course, surface 11 will comprise such combustible material.

In molding a hollow body, molten casting material is introduced into the opening 13 which is coextensive with the longitudinal dimension of the centrifuge head 1 and the article being formed. The cross-sectional dimension of each of the conduits 6 is chosen so as to function as a throttle or metering tube to control the filling of the balancing cavities 5 during the casting process. The size and shape of the conduits are determined by calculations carried out according to known rules of dynamics and depend upon the type of metals to be cast and the casting temperature as well as the asymmetrical shape of the object to be cast. However, tests have shown that a circular conduit with a minimum diameter of at least 8 mm. is desirable. Additionally, the conduits are so shaped that, subsequent to the solidification of the article the conduits and the resulting balancing weights can be removed without adversely affecting the quality of the cast piece. When the molten material for the article is poured into the centrifuge head, and the head rotated, the fluid material will spread uniformly over the surfaces of the pattern more remote from the axis of rotation so that essentially no molten material will flow into the balancing cavities 5 during the initial stages of the casting process. Rotational equilibrium, however, will be maintained since the inwardly projecting portions 14 of the sand mold will tend to counteract any imbalance until the level of the molten material increases to a point radially inwardly towards the axis of rotation where material will commence gradually filling the balancing cavities.

Subsequent to the completion of the molding process and solidification of the cast material, the article 4 is removed from the centrifuge head and the material which has solidified in the balancing cavities 5 and conduits 6 is removed from the article and may be subjected to laboratory investigations to determine the quality of the cast article thus avoiding the necessity of conducting tests on the material of the finished article 4 itself.

It will be understood that various changes and modifications may be made in details of the method and apparatus of the present invention and that the foregoing description relates only to an illustrative embodiment so that various changes in the details of construction and arrangement of parts may be inade without departing from the spirit and scope of the present invention as is defined in the appended claims.

What is claimed is:

1. In a centrifugal casting apparatus of the type having a mold supporting housing mounted for rotation about its longitudinal axis, a casting mold for forming an article having a non-uniform mass distribution with respect to said axis of rotation comprising an interior surface surrounding said axis of rotation and an exterior surface engaging said housing, said interior surface being spaced radially from said axis to form an opening for receiving casting material, said mold having a cavity formed therein adjacent each portion of said interior surface corresponding to a portion of the article to be formed having a reduced mass content with respect to the portion of the article to be formed on the opposite side of the axis of rotation, each cavity having a conduit of predetermined cross-sectional area formed in said mold connecting the interior of each cavity with said opening, each cavity and associated conduit having a volume such that, when casting material is introduced into said opening and the housing rotated, each of the cavities and associated conduits will be filled with a quantity of casting material sufficient to maintain the article being formed in rotational equilibrium with respect to said axis of rotation.

2. The casting mold as claimed in claim '1 wherein each cavity formed in the mold is lined with a pattern forming material which is combustible.

3. The casting mold as claimed in claim 1 wherein each cavity is formed by sheet metal materials which define each cavity in said casting mold.

4. The casting mold as claimed in claim 1 wherein each of said conduits is generally radially disposed with respect to said axis of rotation and each is formed with a cross-sectional area such that the filling of each of said cavities by said casting material will be effected at a rate that is proportional to the rate at which the remaining portions of the mold is filled.

5. The casting mold as claimed in claim 1 wherein each of said conduits is provided with an inlet spaced radially inwardly from the interior surface of said mold. 

1. In a centrifugal casting apparatus of the type having a mold supporting housing mounted for rotation about its longitudinal axis, a casting mold for forming an article having a non-uniform mass distribution with respect to said axis of rotation comprising an interior surface surrounding said axis of rotation and an exterior surface engaging said housing, said interior surface being spaced radially from said axis to form an opening for receiving casting material, said mold having a cavity formed therein adjacent each portion of said interior surface corresponding to a portion of the article to be formed having a reduced mass content with respect to the portion of the article to be formed on the opposite side of the axis of rotation, each cavity having a conduit of predetermined cross-sectional area formed in said mold connecting the interior of each cavity with said opening, each cavity and associated conduit having a volume such that, when casting material is introduced into said opening and the housing rotated, each of the cavities and associated conduits will be filled with a quantity of casting material sufficient to maintain the article being formed in rotational equilibrium with respect to said axis of rotation.
 2. The casting mold as claimed in claim 1 wherein each cavity formed in the mold is lined with a pattern forming material which is combustible.
 3. The casting mold as claimed in claim 1 wherein each cavity is formed by sheet metal materials which define each cavity in said casting mold.
 4. The casting mold as claimed in claim 1 wherein each of said conduits is generally radially disposed with respect to said axis of rotation and each is formed with a cross-sectional area such that the filling of each of said cavities by said casting material will be effected at a rate that is proportional to the rate at which the remaining portions of the mold is filled.
 5. The casting mold as claimed in claim 1 wherein each of said conduits is provided with an inlet spaced radially inwardly from the interior surface of said mold. 